Semi-conductor device and method of making the same



B. Ross 3,062,690

SEMI-CONDUCTOR DEVICE AND METHOD OF MAKING THE SAME Nov. 6, 1962 FiledAug. 5, 1955 l l l 'llllvllllllll 111111,',

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3 with a diiferent activa-ting substance to a desired depth, as Ibyexposure of said surface portions to the activating substance invaporized condition during a selected interval, to thereby constitutethe doped portions of the plate as semi-conductor material of type otherthan that constituting the remaining portions of the plate.

Another important object is to provide a semi-conductor devicecomprising a plate of crystalline semi-conductor material having meansformed on a surface portion of the plate to provide a transistor base,said plate having another surface portion coated with a layer ofmaterial having characteristics different from the remaining portions ofthe plate, said other surface being formed with a continuous groovetherein and extending from one side of the plate to the other, saidgroove extending through said layer and into the body of the platetherebeneath to separate the layer on opposite sides of the groove andto constitute the separated portions of the layer, respectively, -as atransistor emitter and a transistor collector.

The foregoing and numerous other important objects, advantages andinherent functions of the invention will become apparent as the same ismore fully understood from the following description, which, taken inconnection with the accompanying drawings, discloses preferredembodiments of the invention.

Referring to the drawings:

FIG. l is a perspective View showing a semi-conductor device embodyingthe present invention;

lFIG. 2 is a setcional View taken substantially along the line 2 2 inFIG. l;

FIGS. 3 and 4 are similar sectional views taken through modified devicesembodying the invention;

FIG. 5 is a perspective view of another modified device embodying theinvention; and

vFIG. 6 is a sectional view taken substantially along the line 6-6 inFIG. 5.

To illustrate the invention, the drawings show semiconductor devices 11forming transistors, each consisting of a body 112 of crystallinesemi-conductor material and means formed on and operatively associatedwith the body 12 to prov-ide a transistor base '13, and connection means14 and 15, either of which may serve as the emitter element of thetransistor while the other is serving as the collector element thereof.

The body 12 may comprise any suitable semi-conductor material, such `assilicon, lcontaining a selected activating substance distributed throughthe lattice structure of the material rin order to provide desiredsemi-conductor characteristics. Atomic quantities of the activatingsubstance may lbe distributed throughout the material of the body i12 inproportions of the order of one atom of activating substance for everyone hundred million atoms of the intrinsic materiai of the body 12.Arsenic, antimony or other suitable electron donor material may thus lbeemployed as an activating substance to constitute the body 12 as anN-type semi-conductor, while boron, indium or other suitable acceptormaterial may be employed as an activating substance if it be desired toconstitute the body 12 as a P-type semi-conductor.

=The body '12 preferably comprises a relatively thin disc or plate,which may be cut from a crystalline ingot of the selected semi-conductormaterial containing a desired activating substance. Portions 16 of theplate, at and inwardly of a surface thereof, may be treated with anactivating substance other than and diierent from that distributed inthe body 12 of the disc in order to alter the type `of thesemi-conductor material at and to a desired depth inwardly of thebounding surface of the treated portions )16. Where the disc comprisesN-type semi-conductor material, the portions 16 may be treated withboron, aluminum, indium or other electron acceptor substance in order toconstitute the plate portions 16 as P-type semi-conductor material.Conversely, where the disc comprises P-type semi-conductor material, theportions 16 may be treated with arsenic, antimony or other electrondonor substance in order to constitute the plate portions 116 as N-typesemi-conductor material. Preferably, the plate -12 comprises N-typesilicon material embodying arsenic or antimony as the activatingsubstance, the surface portions 16 being treated with boron in order toconstitute the same as P-type semi-conductor material.

The activating substance employed to determine the character of thematerial in the portions 16 may be applied to the surface of the plateand caused to penetrate to a desired depth in said portions by exposingthe plate 12 in an atmosphere consisting of theactivating substance invaporized condition, the plate 12 being retained in such atmosphereduring a period suiicient to obtain penetration of the activatingsubstance to a desired depth at and beneath the surface of the plate.Any suitable, preferred or convenient means may be employed to preventthe application of the activating substance to surfaces other than thoseat which penetration of the substance is desired. It is, however,preferable to expose the entire plate 12 to the vaporized activatingsubstance so that penetration of the activator is obtained at allexposed surfaces of the plate. Thereafter the plate may be ground,milled or etched in order to remove all portions yof the platepenetrated by the activating substance except those portions 16 which itis desired to retain. It will be apparent, of course, that a P-Njunction will thus be established between the boundary of the activatedportions 16 and the remaining portions of the plate 12.

After formation of the activated surface portions 16, the plate 12, ifit comprises N-type semi-conductor material, may be exposed to theaction of vaporized phosphorus 0r other especially active electron donormaterial in order to constitute the remaining surface portions 17 of theplate 12, other than the portions 16, as N+ type semi-conductormaterial, to a desired depth in said other surface portions. Where theconstituent material of the plate 12 comprises P-type semi-conductormaterial, the plate should, of course, be treated with an especiallyactive electron acceptor substance in order to form P-ltype material inthe plate portions 17. It will of course be realized that the N+ or P-i-(as the case may be) surface portions 17 are more heavily doped than thecentral portion of plate 12, and that surface portions 17 in beingheavily doped serve merely as bonding layers or portions to accommodatethe affixing thereto of those layers 18, hereinafter mentioned, whichconstitute base electrodes. After the character of the material in theplate portions 17 has been established to desired depth, portions of theplate may be removed, as by grinding, milling or etching, as indicatedat 19, in order to isolate the activated material comprising portions 17from the material constituting the portions 16. Exposure of previouslytreated portions 16 to vapors of the substance employed to activate theportions 17 will not materially alter the character of the portions 16.If desired, the exposed boundary surfaces of the portions 16 may becoated or otherwise masked by a layer of material that is impervious tothe activating substance, during exposure of the portions 17 to theactivating substance.

In order to protect and also to provide for electrical connection of theactivated plate portions 16 and 17 in external electrical circuits, saidsurfaces may be provided With coating layers 18 of nickel, which may beapplied in any suitable or convenient fashion, as by electrodepositionof the layers or by condensing the layers upon the surfaces to be coatedfrom a vaporized atmosphere of the coating metal. The application ofsuch a layer to the surface of the portions 16, prior to the applicationof an activating substance to the portions 17, will, of course, precludeany contamination of the portions 16 by the activating substance appliedto the portions 17.

In the embodiment illustrated in FIGS. l and 2 of the drawings, asurface portion of the plate 12 may be etched out, as with acid, inorder to provide a shallow depression 19 disposed preferably centrallyof the plate 12 upon the face thereof containing thel activated portions17, the bottom of the depression 19 extending beneath the depth ofpenetration of the activating material to thereby reveal and exposematerial of the plate 12 which is entirely free of the activatingsubstance in the plate portions 17. A suitable etching medium for suchpurpose may comprise a mixture of nitric and hydrofluoric acids.

As shown more particularly in FIGS. 1 and 2, the connection means 14 ofsemi-conductor devices embodying the present invention may comprise analloyed P-N junction in addition to the doped P-N junction formedbetween the constituent material of the plate portions 16 and theremaining portions of the plate. Where plate 12 is initially N-typematerial, this alloyed junction comprises a length of aluminum wire 21having an end penetrating into and alloyed with the material of theplate 12, preferably centrally of the depression 19', such junctionbeing formed by heating the plate 12 and the aluminum wire 21 to atemperature of the order of, but somewhat less than, their meltingtemperatures, and then pressing the end of the wire upon and into theplate to a selected depth at the place where the junction is desired. Asthe end of the aluminum wire becomes alloyed with the material of theplate, it will spread and expand to a limited extent, as shown in FIGS.l and 2, and the alloyed junction will be formed between the plate andwire, said junction comprising recrystallized material of the plate con`taining aluminum dispersed therein. Where plate 12 is initially P-typematerial, wire 21 will comprise donor or N-type material.

The foregoing procedure for the fabrication of transistors allows forevery precise control of the spacement of collector, base and emitter.Such control may be accomplished by regulating the time intervals duringwhich, and the temperature at which, the plate 12 is exposed to thevaporized activating substances in doping the plate portions 16 and 17,If a device should be unsatisfactory due to improper spacing of emitterand collector, the device may be retreated and the wire 21 embedded moredeeply in the plate 12. The ability to thus easily control spacementsmakes it possible to readily attain, in each transistor, precisecharacteristics selected from a wider range thereof.

In FIGURE 3 a transistor device is shown which is similar to that ofFIGURES 1 and 2.. However, in the case of FIGURE 3 the base electrode 18is seen to extend not only on the top surface of plate 12 but also onthe edge surface and on a portion of the lower surface thereof. Theemitter (or collector) electrode layer 1S which is atiixed to thesurface of semiconductor portion 16 is physically separated fromelectrode layer 18 and semiconductor portion 17 by relief area 19.

The device of FIGURE 3 may be fabricated as follows. A disc ofsemi-conductor material may be doped with activating material at thelower surface thereof to provide activated layer 16. The remainingportions of the disc may be masked during this initial operation. Thenthe disc may be ground, etched or milled on the lower surface to removethe peripheral portions of the activated zone 16 and leave only thecentral portion of the disc. The disc may then be doped with activatingmaterial of desired character to a desired depth to provide an activatedportion 17. During this operation the previously doped portion may ormay not be masked, as desired. Finally, the ground, milled, or etchedrelief areas 19 and 19' may be provided (the latter to separateactivated zones or portions 16 and 17) yand the electrode layers 18 andwire 21 affixed in the same manner as that above described.

A modified form of device embodying the invention is shown in FIG. 4,wherein the connection means 14 comprises a doped junction similar tothe connection means 15. In producing the device shown in FIG. 4, a discof material may be doped with activating material to desired depth toprovide activated zones or layers 16 on each of its opposite sides. Thedisc may then be ground, etched or milled on both sides to remove theperipheral portions of the activated zones 16 and leave only theportions of said zones which extend at the medial portions of the disc.The disc may then be doped with activating material of desiredcharacter, to a desired depth to provide an activated zone or layer 17in the peripheral portions of the disc.

The surfaces of the disc may then be electroplated or otherwise coatedwith nickel or other electrical conducting material to provide anelectrical conducting layer 18 on said surfaces. This layer and the bodyof the disc, between the zones 16 and 17 may then be cut away as at 19.If desired, the disc may be coated with a layer of conducting materialafter the formation of the activated zones 16 and before the removal ofthe peripheral portions thereof, to thereby minimize the possibility ofcontaminating the material of the zones 16 with the substance usedsubsequently to activate the zone 17.

Another form of device embodying the invention is shown in FIGS. 5 and6, said device comprising a disc of semi-conductor material 12containing doped layers 16 and 17 of material of unlike electron flowpromoting character on the opposite sides of the disc, a conductinglayer 18 of nickel or other electrical conducting material being coated,as by electrodeposition or other- Wise, upon the surfaces of the layers16 and 17 to facilitate electrical contact therewith. In thisarrangement the layer 17 and its coating 18 may constitute a transistorbase, while the layer 16 may be intersected by a groove 22, extendingfrom one side of the disc to the other, in order to separate the layer16 and its overlying conductive coating 18 into emitter and collectorportions 14 and 15 on opposite sides of the groove. The groove,throughout its length, extends entirely through the layer 16 and itssurface coating 18, and into the material of the disc 12, inwardly ofthe layer 16. The groove is preferably of serpentine character, asshown. It may, however, conveniently be formed to extend diametricallystraight across the disc; or it may have any other preferred layerseparating conliguration.

It is thought that the invention and its numerous attendant advantagesWill be fully understood from the foregoing description, and it isobvious that numerous changes may be made in the form, construction andarrangement of the several parts without departing from the spirit orscope of the invention, or sacricing any of its attendant advantages,the forms herein disclosed being preferred embodiments for the purposeof illustrating the invention.

The invention is claimed as follows:

The method of making an electron flow device which comprises forming adisc of crystalline semiconductor material exhibiting an intrinsicelectrical characteristic, said disc having first and second opposingsurfaces, exposing said disc to a iirst activating substance invaporized condition to obtain atomic penetration for a desired depth bysaid substance of the material of said disc, at and inwardly of saidfirst surface thereo, said first activating substance exhibiting anelectrical character opposite to the intrinsic electrical characteristicof said disc, exposing said disc to a second activating substance invaporized condition to obtain atomic penetration for a desired depth bysaid second substance of the material of said disc, at and inwardly ofsaid second surface thereof, said second activating substance exhibitingan electrical character similar to the intrinsic electricalcharacteristic of said disc, bonding to each of said first and secondsurfaces of said disc iirst and second respective layers of loWresistance metallic substance, thereafter removing atomically penetratedportions in the central portion associated with said first surface ofsaid disc, together With the portion of the metallic layer disposedthereover, to leave an integral layer of atomically pene- @,ceassotrated material encircling said central portion of said disc, and thenfusing a conductor of electrical character opposite to the electricalcharacteristic of said second activating substance to the uncoveredportion of said disc.

References Cited in the tile of this patent UNITED STATES PATENTSPearson Feb. 24, 1953 Dunlap July 7, 1953 10 UNITED STATES `PATENTOFFICE CERTIFICATE 0F CORRECTION Patent Nm 3o6269o November! 6 1962Bernd Ross It is hereby certified that error appears in the abovenumbered patt the said Letters Patent should read as ent requiringcorrection and tha corrected below.

line 3M for "setcional" read M- sectional MU line Column 3y columnSigned and sealed this 28th .day of May 1963l (SEAL) m Attest:

' DAVID L. LADD ERNEST W. SWIDER Attesting Officer Commissioner ofPatents

